| Brucite | |
|---|---|
| General | |
| Category | Mineral |
| Chemical formula | Mg(OH)2 |
| Strunz classification | 04.FE.05 |
| Identification | |
| Color |
white, pale green, blue, gray; honey-yellow to brownish red |
| Crystal habit | platy or foliated masses and rosettes - fibrous to massive |
| Crystal system | Trigonal (Hexagonal Scalenohedral) |
| Cleavage | perfect 0001 |
| Fracture | irregular |
| Tenacity | sectile |
| Mohs scale hardness | 2.5 to 3 |
| Luster | vitreous to pearly |
| Streak | white |
| Diaphaneity | transparent |
| Specific gravity | 2.39 to 2.40 |
| Optical properties | Uniaxial (+) |
| Refractive index | nω = 1.560 nε = 1.580 |
| Birefringence | 0.020 max. |
| Other characteristics | Pyroelectric |
Brucite is the mineral form of magnesium hydroxide, with the chemical formula Mg(OH)2. It is a common alteration product of periclase in marble; a low-temperature hydrothermal vein mineral in metamorphosed limestones and chlorite schists; and formed during serpentinization of dunites. Brucite is often found in association with serpentine, calcite, aragonite, dolomite, magnesite, hydromagnesite, artinite, talc, and chrysotile. Notable locations include Wood's Chrome Mine, Cedar Hill Quarry, Lancaster County, Pennsylvania.
Contents |
Brucite was first described in 1824 and named for the discoverer, American mineralogist, Archibald Bruce (1777–1818). A fibrous variety of Brucite is called Nemalite. It occurs in fibers or laths, usually elongated along [1010], but sometimes [1120] crystalline directions.
Brucite is used as a flame retardant and also constitutes a significant source of magnesium for industry.
When cement or concrete are exposed to non negligible concentration of Mg2+, e.g. when these materials are left in prolonged contact with sea water or brines, Mg(OH)2 precipitates under the high pH conditions prevailing in the cement porewater. The neoformation of brucite, an expansive material, induces mechanical stress in the hardened cement paste and is responsible for the formation of cracks and fissures in concrete.
The use of dolomite as aggregate in concrete can also cause the magnesian attack and should be avoided.